Pro-10 Green Very muddy

[danwojaz]

Hey Everyone,

I have build a few Pro-10 dual overdrives before that were successful. This time, I build the pro-10 green and everything turns on and volume and gain work fine, but the sound is very muddy. I figured that there is an issue with a filtering capacitor, or I used the wrong value capacitor somewhere. I also built another Pro-10 dual overdrive and it has the same issue as the standalone Pro-10 Green overdrive.

Things I did so far.
1. Tested the resistors to see if they were the correct value,
2. Swapped out the OP amps and checked the voltages.
3. Checked the transistors to see if power was going to them.

I will

 

[danwojaz]

I will get pictures of the bottom of the board soon.

 

[danwojaz]

 

[Chuck D. Bones]

What were the results for the things you tried so far?

We can't read half of your caps. Verify C24 is 100pF and not 100nF.

Keep inspecting the board until you find the incorrect part(s).

 

[danwojaz]

@Chuck D. Bones
C4 is 100pf. I just replaced it. I went through and replaced the components in the high pass and low pass areas of the tone pot. It seems like there is another filtering stage that dumps low end in another place. I am checking the caps one by one. it seems the values are correct.


So, I measured all of the resistors and verified their values with the color code.
Measured the op amps
Op1
Pin 1=4.5v
pin2=4.5v
pin3=4.5v
pin4=0v
pin5=4.5v
pin6=4.5v
pin7=4.5v
pin8=9v
op2
Pin 1=4.5v
pin2=4.5v
pin3=4.5v
pin4=0v
pin5=4.5v
pin6=4.5v
pin7=4.5v
pin8=9v

2N5457
pin1=9v
pin2=1.1v
pin3=0v

2n5088
pin1=3.7v
pin2=9v
pin3=9v

 

[Chuck D. Bones]

Opamp voltages are all good. I take it you're rounding off.

Q1 voltages are good.

Q2 voltages are not good. Recheck them. If your measurements are correct then Q2 is blown because the voltage between B & E should never be more than 0.7V.

 

[danwojaz]

@

Opamp voltages are all good. I take it you're rounding off.

Q1 voltages are good.

Q2 voltages are not good. Recheck them. If your measurements are correct then Q2 is blown because the voltage between B & E should never be more than 0.7V.

I swapped it out and now I have

P1=3.69
P2=2.24
P3=9v

 

[danwojaz]

Opamp voltages are all good. I take it you're rounding off.

Q1 voltages are good.

Q2 voltages are not good. Recheck them. If your measurements are correct then Q2 is blown because the voltage between B & E should never be more than 0.7V.

It is still not sounding right. Ill have to play with it some more tomorrow.

 

[Chuck D. Bones]

P1 = E
P2 = B
P3 = C

E & C make sense. What kind of meter are you using to make the measurements? I think it's loading down the circuit because B can't be less than E in that circuit.

 

[danwojaz]

P1 = E
P2 = B
P3 = C

E & C make sense. What kind of meter are you using to make the measurements? I think it's loading down the circuit because B can't be less than E in that circuit.

Sorry it was 4.24

 

[danwojaz]

Sorry it was 4.24

I have a fluke 87 III

 

[Chuck D. Bones]

That's better. We now know that all of the transistors and opamps are biased correctly. It's down to a short, open or incorrect part.

I have a fluke 87 III

That's a goodie.

 

[danwojaz]

@Chuck D. Bones

I have gone through all of the capacitors and verified that they are correct by the writing on the capacitors. I have an original protein and the voltages on the transistors check out and op amps check out.


1. I am wondering if I got a bad batch of components. I built the standalone pro-10 green and dual and they both have the same issue.

2. What are the important capacitors that filter out bass frequencies. When I turn the tone knob, usually it cuts bass frequencies and increases mods and treble. I replaced C11 and that didn’t work.

 

[danwojaz]

@Chuck D. Bones thanks for all of your help. I was a dingus and put a 47k resistor for r21 instead of the 4.7k. It was low passing around 40hz. I forget the exact number.

 

[Chuck D. Bones]

You would not be the first. Good to hear you got it sorted.

47K & 8.2nF make a corner freq at 413Hz. 4.7K moves the corner freq up to 4.1KHz